Verb (it's what you do)
1) The act of removing one's self, usually represented as a label or a tag, from a facebook picture that either depicts the individual under incriminating circumstances or being inebriated while doing something humiliating.
2) The act of coining a weird word like "detag" just so you can sound even remotely cool. Well, this person in particular is cool, regardless.
3) This might actually be a weird Facebook jargon I'm completely unaware of. So...my bad!
Hieu had some pretty revealing pictures of himself on facebook, in which some idiot tagged -- so now the whole world knows about his dirty little secrets. Then he talked to Christine about it and she threw out the word "detag" so that I can untag myself. Problem solved.